I have GROMOS force field parameter of LiTFSI, can i convert into OPLS-AA?

or is there any way to get the OPLS-AA parameters of LiTFSI directly. Thank you!

It is a bad idea to mix and match parameters from different force fields. They have different “strategies” for how to balance charge and Lennard-Jones and more. This is documented in the publications that describe the force fields.

OPLS-AA has publications that describe how the parameters are assigned or new parameters need to be derived.

Actually, I found a paper and they gave the OPLS parameters, I built my TFSI from ATB which has a GROMOS force field where it considers all C as one, all F as one.

While in OPLS it considers every atom a distinct atom.

In short, I also need a data file.

That’s why I am looking for a way to get parameters and data files.

Thank you for your time

some points to consider:

  • you should not use acronyms that are specific to your area of research. I don’t know what you mean by TFSI or ATB. Please see the forum guidelines for explanations how to communicate here and why it is important to avoid domain specific slang terms and acronyms.
  • you should not mix and match different force fields, I mentioned it before and it is still true and the way you argue makes it sound as if you don’t really understand the reason why and how high the risk of getting useless results you are taking
  • you are comparing a “united atom” force field with an “all-atom” force field; bad idea.
  • OPLS comes in two variants, all-atom and united-atom, but even using united-atom OPLS atom types does not solve the problem of mixing and matching different force fields.
  • I don’t understand your reference to a data file in this context. You are discussing much more fundamental issues.

I have nothing to add beyond that. You probably need to obtain personal help from a person with more experience in MD simulations with unusual compounds and the difficulties to get reliable force field parameters. There is not much more information that I can provide short of filling in for your adviser/tutor/supervisor for which I have no time and have no interest in area of research, too.

The Automated Topology Builder is maintained by world-class researchers in Brisbane whom I have the privilege of knowing personally. While I am sure their force fields are generally reasonable, they are primarily geared for quickly parametrising ligands to drug proteins.

Ionic liquids are a hot topic of growing importance. There are plenty of published studies such as https://pubs.acs.org/doi/10.1021/acs.jpcb.1c02189 .

Thank you!
Yes i tried Automated Topology Builder to get force field for TFSI [ bis(trifluoromethanesulfonyl)imide].
it gives GROMOS force field, which is not suitable for this anion. it is Giving 38% error in density.
I read different papers, Mostly they use OPLS force field.
I read one paper, they provided parameters, not data file.
That’s why i am stuck.
I am biggner that’s why confused.

You have to build the data file: it contains the initial structure of your sample in a LAMMPS-specific format.
You can use the all-atom LT file from the ATB website as a starting point and specify the OPLS-AA parameters instead of inheriting them from the GROMOS_54A7_ATB.lt file. This approach requires familiarity with Moltemplate and is off-topic in this forum.